1. Field of the Invention
The present invention relates to apparatus for the manufacture of flat glass wherein the glass is formed while being supported on a surface of a pool of molten metal following delivery thereto as molten glass flowing in a substantially horizontal stream from a glassmaking furnace. More particularly, this invention relates to a combination of elements comprising suitable means for supporting molten glass during its delivery onto such a pool of molten metal.
2. Brief Description of the Prior Art
It is known that molten glass can be delivered onto molten metal and formed into a continuous ribbon or sheet of glass according to the teachings of Heal, U.S. Pat. No. 710,357; of Hitchcock, U.S. Pat. No. 789,911; of Pilkington, U.S. Pat. No. 3,083,501 and U.S. Pat. No. 3,220,816. In all of the prior art, molten glass is delivered over some rigid element, usually a refractory member, onto molten metal. In the practice disclosed by Pilkington, the molten glass is delivered through a long, narrow canal and over a lip from which the molten glass falls onto the molten metal and spreads outwardly on the molten metal. The forming chamber containing the molten metal extends upstream toward the source of molten glass in the apparatus disclosed by Pilkington. In the method of Hitchcock, the molten glass is delivered over a refractory wall onto molten meal contained in a forming chamber adjacent to such a refractory wall downstream of the furnace in which the molten glass is prepared. In the method of Heal, molten glass is delivered over a refractory bridge.
According to the disclosure of Hitchcock in U.S. Pat. No. 1,564,240 the molten metal on which glass is to be formed into a continuous sheet may be contained within a forming chamber comprising a metal casing. As described in U.S. Pat. Nos. 3,584,475 and 3,594,147 to Galey and Sensi, this metal casing may be provided with a refractory liner. Refractory-lined metal casing structures are shown and described in U.S. Pat. No. 3,584,477 to Hainsfurther.
The bottom portion of a typical forming chamber which contains molten metal on which glass is to be formed includes a bottom, side members and end members and is in the form of an open-topped box. A top porition of a typical forming chamber includes a top, sides and end which are sealed to the bottom portion in order to provide an enclosed forming chamber. Because the canal and lip through which and over which molten glass flows prior to being deposited on the molten metal extends above the surface of the molten metal and inwardly from the inlet end of a forming chamber over the molten metal, it is quite easy in a mechanical sense to provide a casing for the bottom portion of a forming chamber such as described by Pilkington, Hainsfurther or Galey and Sensi. Such a casing extends above the intended level for the molten metal pool within such a forming chamber.
According to the teachings of Hitchcock, molten glass is delivered directly through a front wall in a furnace and onto molten metal in an enclosed forming chamber. The front wall of the furnace is a common wall to the enclosed forming chamber, constituting an inlet end wall thereof. Because of the necessarily high temperature of molten glass in the furnace as it is delivered to the enclosed forming chamber, this common wall is necessarily a refractory wall. Such a wall is subject to deterioration during use and it may be readily observed that any leak developing in such a common wall beneath the level of the surface of the molten metal pool within the enclosed forming chamber will result in the loss of molten metal into the bottom of the adjacent glassmaking furnace. This is so since the molten metal is fluid and is more dense than molten glass. In the apparatus of Heal, molten glass is delivered over a refractory bridge. Failure of the downstream wall of the bridge would result in a massive loss of molten metal.
The apparatus disclosed in Heal and that disclosed in Hitchcock are not provided with means for supporting a stream of molten glass for delivery onto molten tin which can be maintained or replaced when worn without requiring a tear-down and replacement of the entire front wall of a glassmaking furnace. As disclosed in a copending application of Charles E. Edge and Gerald E. Kunkle, bearing Ser. No. 455,463, entitled "Flat Glass Manufacturing Apparatus and Method" filed on Mar. 27, 1974, now U.S. Pat. No. 3,893,346 and incorporated by reference herein, it is desirable to provide a means for delivering molten glass from a glassmaking furnace to a glass forming chamber that is sufficiently independent of either the glassmaking furnace or the glass forming chamber so that it may be individually maintained. Thus, it is desirable to provide a molten glass delivery means that includes a bottom portion that effectively extends the bottom portion of the glassmaking furnace and is connected to the bottom of a glass forming chamber. Such a delivery means also includes side members and a roof which is connected to both the glassmaking furnace and the glass forming chamber. The delivery means further includes means for metering the flow of molten glass through it in order to control the rate of glass production.
In the patent of Edge and Kunkle which is incorporated by reference herein, there is a description of a suitable apparatus for delivering molten glass from a glassmaking furnace to a glass forming chamber. Such an apparatus comprises a bottom threshold member, side members of jambs extending upwardly from the threshold member and a metering member extending downwardly toward the threshold member. These elements, in combination, define an opening through which molten glass may flow. The threshold member preferably rests on an extended section of the front wall of a glassmaking furnace and against the inlet end of a glass forming chamber. As will be seen from the description which follows, the present invention provides a threshold member having particularly desirable characteristics.